sed and awk
Henning Schulzrinne
Dept. of Computer Science
sed: string replacement
Line-oriented tool for pattern matching and replacement (stream editor)
Not really a programming language (cf.
awk)
E.g., apply same change to lots of source files
Filter, i.e., does not modify input file
sed description
pattern a text add to output
address s /regex/replacement/
address d delete line
delete lines 1-10: sed -e '1,10d‘
delete comments: sed -e '/^#/d‘
print only matching: sed -n -e '/regexp/p
awk
Special-purpose language for line-oriented pattern processing
pattern {action}
action =
if (conditional) statement else statement
while (conditional) statement
break
continue
variable=expression
print expression-list
awk
Patterns = boolean combinations of regular expressions and relational expressions
awk –f program < input > output
Also delimiter-separated fields:
BEGIN {FS=c}
Examples:
Print lines longer than 72 characters:
length > 72
awk examples
Add up first column, print sum and average
{s += $1 }
END {print “sum is”, s, “average is”, s/NR}
Print all lines between start/stop words:
/start/,/stop/
Print all lines whose first field differs from previous one:
$1 != prev {print; prev = $1}
awk applications
Unix file processing, e.g., as part of a pipe
avoid read loop in shells, Perl
more intuitive syntax than shell scripts
best limited to line-at-a-time processing
